1. Field of the Invention
This invention relates to a coating composition which can cure by exposure to ultraviolet radiation and also has capabilities of curing by exposure to moisture at room temperature. The ability to cure at room temperature provides the coating composition with a characteristic which allows it to be used for coating application where the possibility of exposing all the area of a coated substrate with ultraviolet radiation are so unlikely, so impractical, that one may say it is impossible. This cure process which cures without the exposure to ultraviolet radiation can be termed "shadow cure" or "dark cure" meaning cure which occurs without being exposed to the ultraviolet radiation, i.e. cures in the shadow of the exposure or in the dark areas when the ultraviolet radiation is directed on the substrate.
2. Background Information
Compositions which cure by exposure to ultraviolet radiation are well known in the art, although the number of such materials found in commercial usage today are still relatively small. An even smaller number of such compositions are known to the art which both cure by exposure to ultraviolet radiation and also by another mechanism, such as by heat. Compositions which cure by two mechanisms are said to have dual cure.
Compositions which cure by exposure to ultraviolet radiation and by exposure to moisture, i.e. a dual cure, are also known in the art as shown by Lien et al in U.S. Pat. No. 4,528,081, issued July 9, 1985. Lien et al describe a dual curing silicone composition which contains an acrylic functional dialkoxy or diaryloxy silyl group terminated polyorganosiloxane, an effective amount of a photosensitizer, and a silicone moisture curing catalyst. These compositions of Lien et al can also contain trimethylsilyl terminated silicone oil. Lien et al describe their materials as curing to soft gel like materials or soft rubbery materials. In their examples, the cured materials are defined as a soft rubbery material at 0% oil to a very soft sticky gel at 70% oil which showed a tendency to creep but would not flow.